Preferred parking can be on any floor, but is usually the first two. It is the spaces closest to the escalators or moving walkways. On busier days preferred can be much better. Whenever my family goes to Universal we get preferred, but since we have annual passes it only costs us $6. For regular parking if you arrive after 11am on a weekend, you may be on the roof, which takes forever to get to and from. It really depends on what time you plan on arriving. Anytime before park opening or about 30 minutes after the parks open for regular entry you should be fine to use regular parking.